- Influenza (flu) is a virus that causes people to get sick. Most of the time, the flu causes only a mild illness, but some people can become seriously ill or even die from it. Currently, some pills and inhaled powders can be used to treat the flu, but they only make flu symptoms end about a day sooner. More treatment choices for the flu are needed, especially for those who become seriously ill. Researchers want to test a new drug, AVI-7100, that might keep a person who takes it from having a more serious case of the flu.